Pursuing “augmented reality” and “immersion” screen viewing means of color vividness, high definition display and stereoscopic display. Current display technology has increasingly achieved perfection on vivid color and high definition display, but stereoscopic display. Existing stereoscopic display for naked eye viewing is represented by technical means of non-holographic display and holographic display. Non-holographic display is divided into spatial pattern, meaning of technical solutions by parallax barrier method, lenticular lens method, volumetric matrix method, micro-lens projection method, etc. and time pattern, meaning of technical solutions by micro-retarded plate method, pointing source method, etc. Besides to sacrifice brightness and resolution in exchange for technical means, the downsides of current non-holographic display are: (a) limitation on viewing angle; (b) reduced brightness and resolution; (c) eyes having to maintain the same elevation as the screen; (d) lack of consecutive scenes; (e) crosstalk phenomenon; (f) high cost; (g) less matured contents; (h) viewer dizziness and nausea. The holographic display means of technical solutions by lens holographic method, reflection holographic method, synthetic holographic method, volumetric holographic method, etc., currently, the method of holographic display experiences technical difficulties for wide range of applications.
Human eyes have 3D stereoscopic vision of objects in natural space. The eyes' close side-by-side positioning allows each eye to take a view of the same area of an object from a slightly different angle and thereby creating two offset images known as binocular disparity. The natural 3D stereoscopic vision of human is provided by his brain's combination of two offset images, the brain matching up the similarities and adding in the small differences of the two offset images. The small differences between the two offset images allow the brain to experience 3D stereoscopic perception. Generally, when viewing an object in real space, the viewer's eyes focus and converge onto the object simultaneously; the binocular disparity thereby informs his brain to perceive the depth and location of the object. When viewing a 3D content on a conventional display screen, such as a movie screen, a television screen, a computer screen, a tablet screen, a game console screen, a billboard screen, a portable device screen, a phone screen, or the like, the viewer's eyes behave differently than they do in nature in that they focus on the display screen but converge onto the object appearing in the viewing space and forming parallax. Basically, parallax is a displacement of difference in the apparent position of an object viewed along the two different lines of sight. The parallax informs the viewer's brain that the object viewed on 2D display screen is stereoscopic. In addition, in the viewing space, when image of the viewed object appears to exist between the viewer and the display screen, this effect is known as negative parallax; when image of the viewed object appears to exist behind the conventional display screen, this effect is known as positive parallax. When viewing a 2D content on a conventional display screen, the viewer's eyes also behave differently than he does in nature in that the viewer's eyes focus and converge on the display screen, non-parallax or zero parallax informs the viewer's brain that the objects viewed on the display screen is a 2D image. The zero parallax is effectively strong so as totally weaken the sense of spatial perception despite spatial messages such as space perspective, relative location and relative motion exist, which is known as negative effect to 3D stereoscopic perception by zero parallax. Thus, in order to reproduce spatial perception when viewing a 2D content on a conventional display screen, the technical approach is to eliminate the negative effect by zero parallax.
Human eyes features of binocular accommodation, vergence, and parallax. For a captured scene, the accommodation maps the scene onto the viewer's retina; the vergence combines and processes the left-eye offset image on the left-eye retina and the right-eye offset image on the right-eye retina into one image while avoiding a ghosting effect; the parallax further induces the viewer's perception of spatial location and spatial depth of the scene. While the left-eye image and right-eye images appear certain differences or experiences a spatial displacement, parallax will induce viewer's sense of 3D stereoscopic perception.
FIG. 1 illustrates the imaging principle of 3D stereoscopic vision when viewing objective images on a conventional display screen 4, as well as the effect of image plunge-in or pop-out of the conventional display screen 4. Assuming the interocular distance (the separation space of the eyes) is 1, the conventional display screen 4 is in parallel with the eyes, when the left-eye “L” and the right-eye “R” view the spatial object 30, the left-eye offset image and the right-eye offset image on screen plane 4 are located at corresponding locations 31 and 32. To connect the middle point 2 of the eyes and the spatial object 30, the intersection on the screen plane 4 is 3. For 3D stereoscopic viewing, in one scenario, the binocular accommodation makes the eyes focus onto screen plane 4, the binocular vergence merges the left-eye image 31 and the right-eye image 32 into one image 3. As brain is used to vergence effect, it automatically combines the left-eye offset image 31 and the right-eye offset image 32 into the spatial image 30. Comparing to the image 3 on the screen plane 4, the spatial image 30 possesses spatial depth, thus, it results in 3D stereoscopic vision. The spatial image 30 falls behind the screen 4, it represents the image 3 plunge-in the screen plane 4 (positive parallax). In another scenario, if the image 41 is on the left-eye retina (41=32) and the image 42 is on the right-eye retina (42=31), the brain automatically combines the two images into the spatial image 40. Comparing to the image 3 on the screen plane 4, the spatial image 40 falls in front of screen 4 and represents the image 3 pop-out of the screen plane 4 (negative parallax). In other words, when viewing the spatial object 40, the left-eye offset image and the right-eye offset image on the screen plane 4 are located at the corresponding location 41 and 42, which are defocused (scattered) images. As conventional preparation of 3D stereoscopic content do not take into account the defocusing issue, when making the left eye image 41 and the right eye image 42 on the screen plane 4 by utilizing the focused images 31 and 32, the consequence to viewer's brain is that it extreme lacks of adaptation and causes the viewer dizziness and nausea. Thus, the negative parallax viewing mode is rarely adopted for 3D stereoscopic displays.
Conventional preparation of 3D stereoscopic content is usually divided into pre-production and post-production phases. In the pre-production phase, two designated stereoscopic cameras are used to film the content. In post-production phase, the filmed content is then digitally processed in accordance with the principles of spatial parallax. Usually, the process involves changing the objects in multi-layer of depth of viewing field (normally 4-8 layers) in order to strengthen the 3D effect. This post-production process is also used to convert 2D content into 3D stereoscopic content.
Conventional glasses-free stereoscopic display experiences issues of technical difficulties, less matured 3D contents, crosstalk phenomenon, as well as significantly reducing brightness and resolution, it often causes viewers to suffer eyestrain, headache, dizziness and nausea due to over parallax, excessive convergence and/or divergence. Moreover, frequently switching between divergence and convergence may also cause viewer to perceive deformity, distortion and ghosting of the viewed content.